This invention relates to covering sheaths, for example tubes for covering, generally, elongated substrates such as tubes, rods, wires, and cables, especially tubes, and caps for covering the end of such substrates, and methods for making and using them. 2. DESCRIPTION OF RELATED ART
Harris, U.S. Pat. No. 3,985,951, discloses electrical insulator tubes and caps including a foamable inner layer and an outer layer which may be polymeric and is preferably a heat-shrinkable thermoplastic.
Rehau AG and Co., European Patent Publication No. 0,233,516, discloses a multi-layer plastic shrink tubing for encasing substrates when heat-shrunk over them, where one layer is made of foamable material and the other is not.
Sumitomo Electric Industries, European Patent Publication No. 0 520 473, discloses a multi-layered foam heat-shrinkable tube, having a hot-melt adhesive layer as the innermost layer, and at least one foamable and one non-foamable layer outside the innermost layer.
Sumitomo Electric Industries, European Patent Publication No. 0 713 763, discloses a foamable covering tube, where the inner layer is foamable and the outer layer suppresses outward expansion of the inner layer. The outer layer may, but need not, be heat-shrinkable.
The disclosures of these and other documents referred to throughout this application are incorporated herein by reference.
It would be desirable to develop a covering sheath, for example a tube for covering, generally, an elongated substrate such as a tube, rod, wire, or cable, especially a tube, and a cap for covering the end of such a substrate, having a foamable thermoplastic polymeric inner layer, and a non-foamable non-heat-shrinkable thermoplastic polymeric outer layer surrounding and in intimate contact with the inner layer; the outer layer having a melting point that is at least 60xc2x0 C. above the melting point of the inner layer, and the thickness and mechanical strength of the outer layer being such that the sheath retains substantially constant outer dimensions at a temperature sufficient to cause foaming of the inner layer.
In a first aspect, this invention provides a bi-layer covering sheath, comprising:
(a) a foamable thermoplastic polymeric inner layer, and
(b) a non-foamable non-heat-shrinkable thermoplastic polymeric outer layer surrounding and in intimate contact with the inner layer; the outer layer having a melting point that is at least 60xc2x0 C. above the melting point of the inner layer, and the thickness and mechanical strength of the outer layer being such that the sheath retains substantially constant outer dimensions at a temperature sufficient to cause foaming of the inner layer.
In a second aspect, this invention provides a method of covering an elongate substrate or an end thereof, by placing around that substrate, in the elongate direction, a bi-layer covering sheath of the first aspect of this invention and heating the sheath to a temperature sufficient to cause foaming of the inner layer but not more than the melting point of the outer layer, causing the inner layer to foam, and the sheath to thereby cover the substrate or end thereof.
In a third aspect, this invention provides a method of manufacturing the bi-layer covering sheath of the first aspect of this invention.